Image processing methods for visible and infrared imaging

Abstract

Imaging systems may be provided with image sensors for capturing information about incident light intensities in the visible and infrared bands of light. The means of capturing information about visible light may be unintentionally and undesirably influenced by infrared light. Similarly, the means of capturing information about infrared light may be unintentionally and undesirably influenced by visible light. Storage and processing circuitry may correct for the undesired influence of infrared and visible light on the signal data from the visible and infrared sensors, respectively. The correction may be determined or chosen based on a detection of the illuminant type of the imaged scene. The correction may alternatively be universal, and applicable to images of scenes illuminated by any illuminant.

What is claimed is: 
     
         1 . A method of transforming an input image to an output image, comprising:
 receiving an input signal from an image sensor, wherein the input signal comprises a color input signal that is based on an amount of visible light detected by the image sensor and an infrared input signal that is based on an amount of infrared light detected by the image sensor;   determining a scene illuminant type; and   performing at least one infrared subtraction operation on the color input signal to obtain a color output signal, wherein the infrared subtraction operation is based on the determined scene illuminant type and the infrared input signal.   
     
     
         2 . The method defined in  claim 1  wherein determining the scene illuminant type comprises determining the scene illuminant type based on user input. 
     
     
         3 . The method defined in  claim 1  wherein determining the scene illuminant type comprises determining the scene illuminant type based on the color input signal. 
     
     
         4 . The method defined in  claim 1  wherein determining the scene illuminant type comprises determining the scene illuminant type based on both the color input signal and the infrared input signal. 
     
     
         5 . The method defined in  claim 1  wherein determining the scene illuminant type comprises determining the scene illuminant type based on a proximity of scene illuminant characteristics to those of a plurality of standard illuminants defined by the International Commission on Illumination (CIE). 
     
     
         6 . The method defined in  claim 1  wherein determining the scene illuminant type comprises determining the scene illuminant type based on a proximity of scene illuminant characteristics to those of a plurality of non-standard illuminants. 
     
     
         7 . The method defined in  claim 1  wherein performing the at least one infrared subtraction operation on the color input signal to obtain a color output signal comprises multiplying an input vector by a subtraction matrix, wherein the subtraction matrix is based on the determined illuminant type and wherein the input vector includes values from the color input signal and the infrared input signal. 
     
     
         8 . The method defined in  claim 1 , further comprising:
 multiplying the color output signal by a color correction matrix, wherein the color correction matrix is based on the determined illuminant type.   
     
     
         9 . A method of transforming an input image to an output image, comprising:
 receiving an input signal from an image sensor, wherein the input signal comprises a color input signal that is based on an amount of visible light detected by the image sensor and an infrared input signal that is based on an amount of infrared light detected by the image sensor; and   performing at least one infrared subtraction operation on the color input signal using an infrared subtraction matrix to obtain a color output signal with attenuated infrared light influence.   
     
     
         10 . The method of  claim 9  wherein performing the at least one infrared subtraction operation on the color input image signal using the infrared subtraction matrix comprises multiplying an input vector by the infrared subtraction matrix, wherein the input vector includes values from the color input signal and the infrared input signal. 
     
     
         11 . The method of  claim 10  wherein the infrared subtraction matrix is populated by values that are determined by an optimization framework, wherein the optimization frame work selects matrix values that minimize a difference between a result of preliminary infrared subtraction operation and target color data. 
     
     
         12 . The method of  claim 10  wherein the infrared subtraction matrix is populated by values that are based on a light source deemed most frequently to be encountered in device usage. 
     
     
         13 . The method of  claim 10  wherein the infrared subtraction matrix is optimized for an infrared-rich scene illuminant. 
     
     
         14 . The method of  claim 10  wherein the values that populate the universal infrared subtraction matrix are based or determined by the correction profile for a CIE standard illuminant. 
     
     
         15 . The method of  claim 10  wherein the infrared subtraction matrix is populated by values that are based on an average of infrared subtraction matrices that are optimized for a range of typically encountered light sources. 
     
     
         16 . The method of  claim 9  wherein the input image is based on image data gathered under a scene illuminant and wherein the infrared subtraction matrix is independent of the scene illuminant. 
     
     
         17 . A method of transforming an input image to an output image, comprising:
 receiving an input signal from an image sensor, wherein the input signal comprises a color input signal that is based on an amount of visible light detected by the image sensor and an infrared input signal that is based on an amount of infrared light detected by the image sensor; and   performing at least one color subtraction operation on the input infrared signal using a color subtraction matrix to obtain an infrared output signal with attenuated visible light influence.   
     
     
         18 . The method of  claim 17  wherein performing at least one color subtraction operation on the input infrared signal comprises multiplying an input vector by a subtraction matrix, wherein the input vector includes values from the color input signal and the infrared input signal. 
     
     
         19 . The method of  claim 18  wherein the color subtraction matrix is populated by values that are determined by an optimization framework, wherein the optimization framework selects matrix values that minimize a difference between a result of a preliminary color subtraction operation and target infrared data. 
     
     
         20 . The method of  claim 19  wherein the values that populate the color subtraction matrix are based on a correction profile associated with a standard illuminant defined by the International Commission on Illumination (CIE).